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Post subject: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Tue Jul 10, 2018 12:12 pm
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I am still learning about Tube amps and I was curious to know where and what model tubes does a Fender Blues Jr. 3 uses. Need information for the 2 large tubes and the 3 small tubes.


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Post subject: Re: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Tue Jul 10, 2018 12:34 pm
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Grid21 wrote:
I am still learning about Tube amps and I was curious to know where and what model tubes does a Fender Blues Jr. 3 uses. Need information for the 2 large tubes and the 3 small tubes.

I don't own one of these amps, and I'm no expert, but I did an Internet search for you. The Owner's Manual reads: 2) 6BQ5 and 3) 12AX7 tubes. Here's a copy of the Owner's Manual and welcome to the Forums.
https://support.fender.com/hc/en-us/article_attachments/207301246/Blues_Junior_manual.pdf

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Post subject: Re: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Tue Jul 10, 2018 12:39 pm
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Marky Forrest wrote:
Grid21 wrote:
I am still learning about Tube amps and I was curious to know where and what model tubes does a Fender Blues Jr. 3 uses. Need information for the 2 large tubes and the 3 small tubes.

I don't own one of these amps, and I'm no expert, but I did an Internet search for you. The Owner's Manual reads: 2) 6BQ5 and 3) 12AX7 tubes. Here's a copy of the Owner's Manual and welcome to the Forums.
https://support.fender.com/hc/en-us/article_attachments/207301246/Blues_Junior_manual.pdf


Cool thanks, also, is there such a thing as overdriving a tube amp in the sense of I push so much of a clean signal from a guitar pedal that it makes the tube "break up" and distort and is that a bad thing? Or pretty normal?


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Post subject: Re: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Tue Jul 10, 2018 12:49 pm
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Post subject: Re: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Tue Jul 10, 2018 1:02 pm
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Grid21 wrote:
Marky Forrest wrote:
Grid21 wrote:
I am still learning about Tube amps and I was curious to know where and what model tubes does a Fender Blues Jr. 3 uses. Need information for the 2 large tubes and the 3 small tubes.

I don't own one of these amps, and I'm no expert, but I did an Internet search for you. The Owner's Manual reads: 2) 6BQ5 and 3) 12AX7 tubes. Here's a copy of the Owner's Manual and welcome to the Forums.
https://support.fender.com/hc/en-us/article_attachments/207301246/Blues_Junior_manual.pdf


Cool thanks, also, is there such a thing as overdriving a tube amp in the sense of I push so much of a clean signal from a guitar pedal that it makes the tube "break up" and distort and is that a bad thing? Or pretty normal?

In my experience, humbuckers will make amps break up sooner than single coils. It is normal for tube amps to only have a limited volume for about half to 3/4 of the volume control, after that the output becomes saturated and you get more compression/distortion. If you think it needs more headroom, you can change preamp valves or use a different rating power valves to make it stay cleaner longer.
That being said, I am not one of the amp experts on this Forum. Maybe one of them will chime in. 8)

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Post subject: Re: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Tue Jul 10, 2018 6:53 pm
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Marky Forrest wrote:
2) 6BQ5

Known more commonly as "EL84"
It is not a 40w amp... closer to 15w. The max draw from the mains is 180w.

Fender does tend to bias the BJ pretty "hot", so when you replace the tubes, make sure it is with a matched set, and after powering on, watch closely and make sure that the tubes are not red-plating. This is not extremely common, but it does happen, and it can damage the tubes, as well as burn out other circuitry in the amp.
Some believe that ANY time you change the tubes, you should have the amp professionally biased.

Is there any particular reason that you are changing the tubes? Does the amp no longer function, or are you thinking that it will improve the sound?

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Post subject: Re: Tubes for a Fender Blues Jr. 3 40Watt
Posted: Wed Jul 11, 2018 12:59 am
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CB91710 are right about power tubes


From billm Audio pages;

http://billmaudio.com/wp/?page_id=131
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http://billmaudio.com/wp/?page_id=1155

Setting the Bias

After you’ve installed the basic mods, your final task is to set the bias. Much mystery seems to surround setting the bias, but it’s really quite simple. Bias controls the current flowing through your output tubes, and it’s well known that the Blues Junior’s original designer chose a large current, or hot bias. This causes excessive tube wear, limits headroom, and constrains the tonal range of the amp.

Each model of output transformer has a characteristic resistance and when current flows through it to power the tubes, there is a voltage drop across the resistance. All you have to do is measure across two leads of the transformer and adjust the bias trimmer potentiometer until you get the correct voltage.

This video, showing a Blues Junior with EL84s and a TO20 output transformer, demonstrates how easy it is to set the bias.


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